The present invention relates to a method of arraying self-scanning light-emitting element array chips, in which it is possible to remove defective chips. The present invention further relates to a self-scanning light-emitting device comprising a plurality of chips arrayed by said method, and a method of removing defective chips from arrayed chips.
A self-scanning light-emitting element array chip has a characteristic such that the number of bonding pads is more less than that of a conventional light-emitting element array chip. Due to this characteristic, the size of a chip may be effectively small. For example, if bonding pads are provided at both ends of a rectangular chip, the width of the chip may be short to that required only by bonding pads themselves. However, when a plurality of self-scanning light-emitting element chips are arrayed in a straight line manner to form a self-scanning light-emitting device used for an optical printer head, an array pitch of light-emitting elements can not be constant at the ends of the neighboring chips. In order to avoid this, a plurality of chips are arrayed in a zigzag manner such that the ends thereof are overlapped (see Japanese Patent Publication No. 8-216448).
FIG. 1 shows a schematic drawing for explaining a method of arraying chips in a zigzag manner. For assistance of explanation, an x-y coordinate axis is designated in the figure. An x-axis direction shows an array direction of chips and a y-axis direction perpendicular thereto.
At the both ends of a self-scanning light-emitting element array chip 10, there are provided bonding pads 12 between thereof a plurality of light-emitting elements 14 are arrayed in a straight line manner. A plurality of self-scanning light-emitting element array chips 10 are arrayed and fixed by means of an adhesive on a substrate (not shown in the figure) in a zigzag manner in an x-axis direction, i.e. in such a manner that the ends of neighboring chips are overlapped in a y-axix direction. According to this method, an array pitch of the light-emitting elements may be constant through all of the chips.
A few chips may be defective by any reason after a die bonding process and wire bonding process to the chips arrayed on the substrate. In this case, it is not effective in cost to discard the substrate itself thereon the defective chips are mounted. Therefore, the method is adopted such that only defective chips are removed and replaced by normal chip. In fact, the defective chip is removed in such a manner that a metallic tool is push against the side of the chip. In the conventional chip array in a zigzag manner, neighboring chips are overlapped at their ends in a y-axis direction. In order to remove one chips in the conventional chip array, that one chip only must be push by means of a narrow metallic tool 16 as shown in FIG. 1. A light-emitting element array chip is generally made of fragile compound semiconductor such as GaAs. Therefore, when a force is applied to a part of the defective chip fixed on the substrate by an adhesive, the chip is generally crushed leaving a portion of the chip overlapped in a y-axis direction on the substrate. It is quite difficult to remove the left portion without damaging the neighboring chips.
An object of the present invention is to provide a method of arraying self-scanning light-emitting element array chips, in which it is possible to remove defective chips completely.
Another object of the present invention is to provide a self-scanning light-emitting device comprising a plurality of self-scanning light-emitting element array chips arrayed by said method.
A further object of the present invention is to provide a method of removing defective chips.
A first aspect of the present invention is a method of arraying a plurality of self-scanning light-emitting array chips in a zigzag manner on a substrate, each chip being rectangular and comprising an array of light-emitting elements arrayed in a line facing to one end of the chip and a plurality of bonding pads provided on the other end of the chip. In this method, the plurality of chips are arrayed in such a manner that one ends of neighboring chips are arranged without overlapping in an array direction of chips so that an array pitch of chips is constant, and the other ends of the chips are arranged with overlapping in a direction perpendicular to an array direction of chips so that an array pitch of chips is constant.
Each self-scanning light-emitting element array chip comprises an array of transfer elements having such a structure that a plurality of three-terminal transfer elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the transfer elements neighbored to each other are connected via first electrical means, a power supply line is connected to the control electrodes via second electrical means, and a clock line is connected to one of two terminals except the control electrode of each of the transfer elements; and the array of light-emitting elements having such a structure that a plurality of three-terminal light-emitting elements each having a control electrode for controlling threshold voltage or current are arranged.
A second aspect of the present invention is a self-scanning light-emitting device comprising a plurality of self-scanning light-emitting array chips which are arranged by the method of arraying the plurality of self-scanning light-emitting array chips in a zigzag manner on a substrate.
A third aspect of the present invention is a method of removing a defective chip in a plurality of self-scanning light-emitting array chips arrayed on a substrate by the method of arraying the plurality of self-scanning light-emitting array chips in a zigzag manner on a substrate. In this method, the defective chip is removed together with a chip overlapped with the defective chip in a direction perpendicular to an array direction of chips by applying force to one side of the defective chip or the chip overlapped therewith in a direction perpendicular to an array direction of chips.